#1 don't use the dock hose, but a good quality potable water hose
#2 Let the water run long enough that it tastes good out of the hose. many marinas have a mike of plastic pipe and if not enough water goes through it you wil have a problem. I am at the end of the dock so I have to let the water run 2 to 3 minutes then taste and smell it before putting aboard.
If you do not use a lot of water buy an additive or dump the tank once a week. i use a tank in 3 to 4 days (the shower uses a lot) so followiing the steps above, I have good potable water.
lastly, don't put potable antifreeze in your tank, pump it dry and put a couple of tblsps of the additive above. Unhook the hose and pump the antifreeze through lines only.
Mike